The present invention relates to a voice communication system and method in communication terminals connected through a communication network.
As a conventional voice communication system, there is known a system which uses a line switching procedure through a line switching network such as a telephone network. For example, the standard thereof is indicated in CCITT (International Telegraph and Telephone Consultative Committee) Recommendation, ISDN, Q. 937. In this system, a communication terminal (telephone) connected to the line switching network transmits a voice communication request to a switching center dedicated to line switching processing, and the switching center receiving the request performs voice communication control for communication with a communication terminal (telephone) of the other party. Voice information sent at a constant speed is continuously transmitted and received through the switching center even during the voice communication.
In a packet switching network such as LAN (Local Area Network), in turn, the communication control is directly performed between communication terminals for transmitting and receiving packets. For example, Etherphone using Ethernet is well known.
However, due to the difference in schemes between the packet switching network and the line switching network, conventional voice communication systems such as that using the telephone network and so on cannot be utilized for realizing voice communication between communication terminals connected to the packet switching network.
To cope with this problem, a system for editing voice information into packets for transmission and reception between communication terminals has been proposed for adapting the voice communication scheme for communications between communication terminals connected to the packet switching network to the line switching network. However, even if the line switching network is connected with the packet switching network, a direct voice communication is not permitted between a communication terminal supporting voice communications between communication terminals connected to the packet switching network and a telephone connected to the line switching network and supporting the conventional voice communication function. This is due to the difference between the voice communication protocol of the packet switching network and the conventional voice communication protocol.